In 1876, inside a third floor walk-up garret apartment in the Scollay Square section of Boston Mass., Alexander Graham Bell spoke the first sentence transmitted over telephone wires. Technical innovations have dramatically transformed the telecommunications industry over the past one hundred and twenty three years. For example, telecommunications switching systems have evolved considerably from “hand operated” systems in which one instrument was electrically connected (through a hierarchical switching network) to another through the intervention of a human operator who would physically plug one circuit into another. Such direct electrical connection of two or more channels between two points (at least one channel in each direction), a connection that provides a user with exclusive use of the channels to exchange information, is referred to as circuit switching, or line switching. Human operators have largely been replaced by systems which employ electronic switching systems (ESS), in which the instruments are automatically connected through the network by electronic systems.
Additionally, in many cases, the signalling system employs optical signalling instead of, or in addition to, electronic signalling. Nevertheless, such switching systems often still employ circuit switching, a technique which yields highly reliable service, particularly for such “real time” communications applications as voice, in which the momentary loss of a channel is annoying and repeated such losses are unacceptable. Switching systems may interconnect telephone instruments through circuit switching, employing time division multiplexing (TDM), for example. The switching system may carry digitized telecommunications signal over optical paths that are in conformity with synchronous optical network (SONET) standards. Such networks include network elements such as SONET network elements, SDH network elements, or wavelength division multiplexed network elements, for example. Circuit switching network elements include any network elements which conform with SONET/SDH signal formats. The signal formats are described, for example, in a Technical Advisory entitled “Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria,” TA-NWT-000253, Bell Communications Research, Issue 6, September 1990, which is hereby incorporated by reference. For a variety of reasons it may be important to know which port in a given network element (NE) within such a system is connected to a particular port of another NE within the system.
Although SONET systems may incorporate a facility for such port identification and network elements within a circuit switching telecommunications system may employ this facility to identify ports, network elements within a packet switching system do not typically provide for port identification. That is, a technique known as packet switching may be employed for the transmission of data over telecommunications network. With packet switching data is transmitted in packets, and the communications channel is only occupied for the duration of a packet's transmission. After the transmission, the channel is available for use by other packets being transferred for other users. The packetized transmission may be transmitted using asynchronous transfer mode (ATM) techniques, for example. Asynchronous transfer mode (ATM) is a connection-oriented transmission technique that employs fixed-size blocks of data, called cells, each of which consists of a five octet long header and an information field that is forty-eight octets long. Packet switching network elements, such as ATM nodes or Internet Protocol (IP) routers, typically ignore the SONET signalling that might otherwise be employed to identify specific interconnected ports within a telecommunications network. Consequently, operator intervention may be required to accomplish such identification. Such a process would be time consuming, fraught with the potential for errors, and cost-prohibitive. Systems that employ both circuit switching and packet switching network elements and which employ SONET signalling may be referred to hereinafter as heterogeneous telecommunications systems. A heterogeneous telecommunications system that provides for automatic port identification would therefore be highly desirable.